A method for preparing a high-thermal-conductivity diamond film substrate for a semiconductor

Abstract

The application provides a preparation method of a high-thermal-conductivity diamond film substrate for semiconductors, and relates to the technical field of diamond film growth preparation and processing. The preparation method prepares the high-thermal-conductivity diamond film substrate for semiconductors with high comprehensive performance through the preparation and surface treatment of a substrate, high-density preferred orientation diamond grain nucleation, periodic nucleation + diamond film deposition, substrate and diamond film stripping, and surface grinding, polishing and cleaning. The main technology used is high-density preferred orientation diamond grain nucleation + periodic nucleation, and the diamond substrate includes a preferred orientation high-density grain layer formed by high-concentration methane nucleation, a preferred orientation high-density grain layer formed by high-concentration methane growth, and periodic nucleation grains. The method is simple and easy to operate, low in cost and energy consumption, and high in efficiency, and is conducive to industrial large-scale production and promotion.

Description

Technical Field

[0001] This invention relates to the technical field of diamond film growth, preparation and processing, and in particular to a method for preparing a high thermal conductivity diamond film substrate for semiconductors. Background Technology

[0002] High-quality semiconductor substrate materials are fundamental to the development of high-performance electronic devices, and their performance directly determines the performance of semiconductor devices. Compared to traditional substrate materials, diamond is an ideal semiconductor substrate material, possessing an ultra-wide bandgap (5.47 eV), a low dielectric constant (5.7), and a high resistivity (>10). 12 Diamond has the characteristics of Ω·cm, and its thermal conductivity at room temperature can reach more than 2000 W / (m·K). Compared with silicon, a conventional semiconductor material, diamond's excellent thermal conductivity can remove the heat generated during device operation in a timely manner, which can greatly improve the device's operational safety and lifespan. Its high resistivity can reduce parasitic current, improve the stability of high-frequency or high-power devices, and give full play to the device's performance. In addition, some studies have shown (Zhu Hongxi, Mao Weimin, Feng Huiping. The Influence of Texture on Residual Strain of CVD Self-Supported Diamond Film [J]. Journal of Materials Research, 2007, (01): 32-36.) that for polycrystalline diamond films, a (110) / (100) preferred orientation on the polished surface can reduce the residual compressive stress and residual strain of the film, which is beneficial to the spread of surface semiconductor devices. At present, the mainstream diamond preparation methods are high temperature and high pressure (HTHP) and chemical vapor deposition (CVD). Among them, chemical vapor deposition has become the mainstream method for preparing diamond semiconductor substrates due to its advantages such as high pressure resistance, high radio frequency, low cost, and high temperature resistance. For polycrystalline diamond prepared by CVD, it is currently possible to prepare polycrystalline diamonds of 4 inches and above.

[0003] For polycrystalline diamond prepared by CVD, it is currently possible to prepare polycrystalline diamonds of 4 inches and above. However, during the deposition process of CVD polycrystalline diamond, as the thickness increases, due to the competitive growth of grains, it usually exhibits a columnar crystal state, and the grains become coarse. The grain boundaries become more obvious with the increase of thickness. By using an optical microscope to observe the polished diamond film, many dark spots or irregular pores can be observed on the polished surface and inside the film. Grain boundaries are the main source of these defects. The morphology, number and distribution of defects on the polished surface will affect the spread of semiconductor devices on the polished surface, while defects inside the diamond will affect the overall performance of the diamond substrate, thereby affecting the performance of semiconductor devices. On the other hand, CVD polycrystalline diamond films are usually oriented randomly, and there is a lot of residual stress on the polished surface, which will affect the spread of semiconductor devices.

[0004] For example, Chinese patent CN102157353A discloses a method for preparing a diamond substrate for high thermal conductivity integrated circuits. The semiconductor diamond substrate prepared by this method has a thickness of less than 1 mm and a high surface roughness. Furthermore, the process is only applicable to DC arc plasma jetting and cannot cover multiple methods for preparing diamond substrates.

[0005] Chinese patent CN111009496A discloses a semiconductor substrate with high thermal conductivity and its preparation method. The semiconductor substrate has a periodic hole structure on its back side, and a diamond film is embedded in the periodic hole structure. The surface of the diamond film is flush with the back side of the semiconductor substrate to form a periodically distributed diamond film pattern. This semiconductor substrate preparation method utilizes the high thermal conductivity of diamond and combines it with traditional semiconductor substrate materials. However, the preparation method is relatively complex, technically difficult, and cannot fully utilize the ultra-high thermal conductivity of the diamond substrate.

[0006] Chinese patent CN119776984A discloses a method for preparing a high thermal conductivity diamond polycrystalline substrate. The method uses a multi-temperature gradient deposition of the high thermal conductivity diamond polycrystalline substrate. The maximum temperature difference during the deposition process of this polycrystalline diamond substrate is 400°C, which increases the formation of microcracks inside the diamond, is not conducive to stable growth, increases the probability of substrate cracking, and makes process control difficult. Summary of the Invention

[0007] The main objective of this invention is to address the technical problems existing in the CVD method for preparing polycrystalline diamond substrates, such as poor crystal quality leading to low thermal conductivity, numerous surface pores after polishing, poor flatness, and high surface stress. Therefore, a method for preparing a high thermal conductivity diamond film substrate for semiconductors is proposed, which solves the aforementioned problems. By using a high-frequency periodic nucleation method during the growth stage, and after grinding and polishing the diamond film nucleation surface, a high thermal conductivity semiconductor diamond film substrate with high grain density, low surface roughness, low surface defects, and low surface residual stress can be obtained.

[0008] The technical solution is as follows:

[0009] A method for preparing a high thermal conductivity diamond film substrate for semiconductors, the method comprising the following steps:

[0010] S1. Substrate preparation and surface treatment: First, the substrate on which the diamond film is deposited is surface treated. Then, a nanodiamond suspension is used to electrostatically seed diamonds on the substrate surface. Finally, the surface-treated substrate is cleaned and dried to obtain the surface-treated substrate.

[0011] S2. High-density preferred orientation grain nucleation: The substrate with surface treatment completed in S1 is placed in a chemical vapor deposition apparatus, vacuumed, and heated. After heating to the preferred orientation grain nucleation temperature, high-density preferred orientation diamond grain nucleation is performed on the substrate surface. After nucleation, the methane gas flow rate is adjusted to 1-3% of the total gas flow rate, and 0.1-0.3% carbon dioxide gas is introduced simultaneously. High-density grain growth of the nucleation layer is performed on the basis of the high-density preferred orientation diamond grain, resulting in a high-density nucleation layer on the substrate surface.

[0012] S3, Periodic nucleation + diamond film deposition: Deposit diamond on the high-density nucleation layer on the substrate surface of S2 for 12-24 hours, and then start periodic nucleation and diamond film deposition to obtain a substrate with a diamond film layer.

[0013] S4. Separation of substrate from diamond film: Cool down the substrate with diamond film layer from S3, turn off the machine, and after cooling to room temperature, separate the substrate from the diamond film to obtain a diamond film with diamond nucleation layer.

[0014] S5. Surface grinding, polishing and cleaning: The surface of the nucleation layer of the diamond film with diamond nucleation layer in S3 is mechanically ground and polished, and the polished diamond film is cleaned to finally obtain a high thermal conductivity diamond film substrate for semiconductors.

[0015] Optionally, the diameter of the substrate in S1 is 100-200mm and the height is 10-50mm; the substrate includes ordinary commercial graphite substrate, Mo substrate and Si substrate. The following are the surface treatment methods for the three substrates: 1) Ordinary commercial graphite substrate: After the ordinary commercial graphite substrate is planarized, a Ti metal transition layer is deposited on the surface. Metal Ti is sputtered using a magnetron sputtering instrument for 10-15 minutes, with Ar as the protective gas. Then, annealing heat treatment is performed in a vacuum furnace for 30-40 minutes at a temperature controlled at 800-900℃, and the furnace is cooled; 2) Mo substrate and Si substrate: The substrate surface is planarized and polished.

[0016] Optionally, the diamond electrostatic seeding process in S1 is as follows: the substrate with deposited diamond film is immersed in a nanodiamond suspension with a concentration of 2.5-5.0wt%, and removed after standing for 15-20 minutes; the cleaning and drying process is as follows: anhydrous ethanol is used for cleaning to rinse away the diamond residue on the substrate surface; the drying process is to place the substrate in a resistance furnace, heat it at 150-180℃ for 120-180 minutes, and then cool it with the furnace.

[0017] Optionally, the chemical vapor deposition apparatus in S2 includes a DC arc plasma CVD apparatus, a microwave plasma CVD apparatus, and a hot filament CVD apparatus; vacuuming and heating the substrate: after evacuating the deposition apparatus chamber to less than 0.5 Pa, pure hydrogen gas with a purity of 99.9999% or higher is introduced at 1-7000 sccm, and argon gas at 0-7000 sccm. The power and chamber pressure are adjusted, and the chamber pressure is maintained at 3.0-12.0 kPa. The substrate is heated at a rate of 3-5 °C / min.

[0018] Optionally, the nucleation temperature of the preferred orientation grains in S2 is 820-860℃; the high-density preferred orientation diamond grain nucleation process is as follows: 1) Nucleation of <110> oriented grains: The substrate temperature is raised to 820-830℃, and 2-3% of methane is introduced into the total gas flow rate to carry out high-density grain nucleation for 30-40 minutes, maintaining the temperature at 850-860℃, and the grain thickness reaches 10-20μm; 2) Nucleation of <100> oriented grains: In a chemical vapor deposition equipment... A tungsten electrode is designed below the plasma discharge cathode. A DC pulse power supply with a voltage of 200-300V and a current of 1-2A is connected between the substrate and the tungsten electrode. The substrate is connected to the cathode, and the tungsten electrode is connected to the anode of the pulse power supply. The substrate temperature is raised to 820-830℃, and 2-3% of methane in the total gas flow rate is introduced to carry out nucleation for 20-30 minutes. The temperature is maintained at 850-860℃, and the grain thickness reaches 10-20μm. After nucleation is completed, the pulse power supply is turned off.

[0019] Optionally, the high-density grain growth conditions of the nucleation layer in S2 are as follows: maintain the flow rates of pure hydrogen and argon at a constant level, change the flow rate of methane to 1-3% of the total gas flow rate, and simultaneously introduce 0.1-0.3% carbon dioxide gas, adjust the cavity pressure to maintain 3.0-12.0 kPa, and keep the substrate temperature above 1100°C for diamond deposition for 12-24 hours.

[0020] Optionally, the periodic nucleation and deposition process of the diamond film in S3 is as follows: after the dense grains of the nucleation layer grow for 12-24 hours, periodic nucleation begins, with an interval of 24-36 hours between two nucleations. Methane at 2.5-4% of the total gas flow rate is used for nucleation for 30-40 minutes. After one nucleation, the methane is adjusted to 1.3-1.5% of the total gas flow rate for deposition for 4-8 hours, and then the methane is adjusted to 1-1.3% of the total gas flow rate for deposition until the next nucleation. This process is repeated several times, with a total deposition time of 300-600 hours, so that the diamond film deposition thickness is greater than 1 mm. During the above process, 0.1-0.3% carbon dioxide gas is introduced and kept constant.

[0021] Optionally, the interlayer structure of the substrate with diamond film in S3 is a 10-20 μm thick <110> / <100> oriented high-density nucleation grain layer and a 70-120 μm thick <110> / <100> oriented high-density grain layer. After the formation of the high-density nucleation grain layer, a short-time high-concentration methane grain layer is grown to ensure that the nucleation surface remains <110> / <100> oriented after grinding and polishing, thereby reducing surface stress and surface porosity and improving surface quality.

[0022] Optionally, the cooling process in S4 is as follows: after the diamond film thickness is greater than 1mm, the power of the device is reduced by reducing the current, and the cooling rate is controlled at 1-3℃ / min, so that the temperature is reduced by 30-50℃, and then held for 30-50min.

[0023] Optionally, the interlayer structure of the diamond film with diamond nucleation layer in S4 is a 10-20 μm thick <110> / <100> oriented high-density nucleation grain layer, a 70-120 μm thick <110> / <100> oriented high-density grain layer, and an 800-1500 μm thick periodic nucleation grain, with the interlayer structure distributed from the substrate upwards according to the process sequence.

[0024] Optionally, the mechanical grinding and polishing in S5 is as follows: the diamond film growth surface is fixed on a grinding fixture, and the nucleation surface is thinned using W40 diamond micropowder with an average particle size of 30 μm, W20 diamond micropowder with an average particle size of 15 μm, W10 diamond micropowder with an average particle size of 10 μm, W5 diamond micropowder with an average particle size of 3.5 μm, and W1 diamond micropowder with an average particle size of 1 μm. Each is ground for 0.5-2 hours to reduce coarse particles on the surface. During this time, the grinding disc rotation speed is 40-60 r / min, the linear velocity is 0.8-1.2 m / s, and the load pressure is 0.1 MPa. Then, the diamond film is placed in a polishing disc, and the nucleation surface is polished at a rotation speed of 1000-1200 r / min and a load of 0.20 MPa for 100-200 hours until the surface roughness is less than 1 nm.

[0025] Optionally, the cleaning process in S5 is as follows: boil the polished diamond film with concentrated H2SO4 and concentrated HNO3 at a volume ratio of 4:1 for 20-40 minutes; then rinse the surface with deionized water to remove residual acid, and then ultrasonically clean the sample with acetone and anhydrous ethanol for 10-30 minutes respectively, and blow dry.

[0026] Optionally, in S5, the nucleation layer thickness of the high thermal conductivity diamond film substrate for semiconductors is reduced by 10-30 μm compared to before mechanical polishing. The thermal conductivity of the high thermal conductivity diamond substrate for semiconductors is 2000-2300 W / m·K, the surface roughness Ra is 0.4-0.95 nm, and the resistivity is 8.5-56 × 10⁻⁶. 13 Ω·cm, flexural strength is 500-600MPa.

[0027] The key technical point of this invention is:

[0028] 1. In order to obtain a complete and crack-free diamond film, the substrate on which the diamond film is deposited is first processed. For graphite substrates, a Ti metal transition layer needs to be deposited on the substrate surface to ensure good bonding between the diamond film and the substrate during the growth process. During the cooling process, the transition layer and the diamond film are effectively separated. For Mo and Si substrates, only polishing is required to make them flat.

[0029] 2. To increase the grain density of the nucleation surface, polishing the diamond film nucleation surface can yield a surface with fewer defects, and a higher methane concentration can be used for grain nucleation. At a high methane concentration of 2-3%, the preferential growth of large grains can be suppressed, and the initially nucleated small grains can be retained. Too low a methane concentration will produce columnar large grains, resulting in an increase in surface porosity.

[0030] 3. In order to improve the overall quality of diamond film and make the final product diamond film substrate have high thermal conductivity and high volume resistivity, high-frequency periodic nucleation is carried out during the diamond film deposition process. Through the deposition-nucleation-deposition method, the traditional columnar crystal growth law of diamond film growth is broken and equiaxed crystal growth is achieved.

[0031] Furthermore, during the deposition process of CVD polycrystalline diamond, as the thickness increases, due to the competitive growth of grains, it usually exhibits a columnar crystal state, with the grains becoming coarser and the grain boundaries becoming more pronounced with increasing thickness. By proposing a method of high-frequency periodic nucleation during the diamond film growth stage, through a deposition-nucleation-deposition approach, the traditional columnar crystal growth pattern of diamond films is broken, and equiaxed crystal growth is achieved, thereby improving the overall quality of the diamond film and reducing defects.

[0032] The above technical solution has at least the following advantages compared with the existing technology:

[0033] The present invention proposes a method for preparing a high thermal conductivity diamond film substrate for semiconductors. By increasing the grain density on the nucleation surface, refining the grains, reducing surface defects and residual stress, and performing high-frequency periodic nucleation during the diamond film growth stage, the traditional columnar crystal growth pattern of diamond films is broken, and equiaxed crystal growth is achieved, thereby improving the overall quality of the diamond film and reducing diamond defects. Therefore, it can solve the technical problems existing in the CVD method for preparing polycrystalline diamond substrates, such as poor crystal quality leading to low thermal conductivity, numerous surface pores after polishing, poor flatness, and high surface stress.

[0034] This invention selects a wide range of substrates and deposition equipment for depositing diamond films. The substrates for depositing diamond films include graphite substrates, Mo substrates and Si substrates. The deposition equipment includes DC arc plasma jet CVD (DC arc plasma jet CVD) devices, microwave plasma CVD (MPCVD) devices and hot filament CVD (HFCVD) devices. It is widely applicable and the process is simple and controllable.

[0035] The method of this invention achieves self-peeling of diamond film from substrate by treating the substrate surface and depositing Ti on graphite substrate; it also achieves self-peeling of diamond film from substrate by polishing Mo and Si substrates, thereby improving preparation efficiency and success rate.

[0036] The method of the present invention performs diamond electrostatic seeding on the substrate surface, forming uniform micro-scratches on the substrate surface, which facilitates subsequent diamond deposition and improves the uniformity of diamond growth.

[0037] The method of this invention enables the formation of 10-20 μm <110> oriented grains on a substrate by nucleating high-density preferentially oriented diamond grains at 820-830°C with 2-3% methane of the total gas flow rate; and by using bias nucleation technology at 820-830°C with 2-3% methane of the total gas flow rate, the formation of 10-20 μm <100> oriented grains on a substrate.

[0038] The method of this invention involves growing the grains in 1-3% methane for 12-24 hours after nucleation, while simultaneously introducing 0.1-0.3% carbon dioxide gas. This results in a high-density, preferentially oriented grain layer of 80-140 μm. After grinding and polishing, the surface remains in the <110> / <100> orientation, resulting in a polished surface with low surface stress, reduced surface porosity, and a roughness as low as 1 nm. The carbon dioxide gas can also etch and refine the grains.

[0039] The method of this invention, through periodic nucleation and diamond film deposition, can reduce the competitive growth of grains during diamond growth, which leads to grain coarsening, thereby reducing internal defects in the diamond and improving the overall quality of the diamond film.

[0040] The method of the present invention can completely obtain a crack-free self-supporting diamond film by peeling the substrate from the diamond film.

[0041] The method of the present invention, through surface grinding, polishing and cleaning, can obtain a clean and uncontaminated high-grain density, low surface roughness, low surface defects and low surface residual stress high thermal conductivity semiconductor diamond substrate.

[0042] In summary, compared with traditional methods, the method of this invention prepares a high thermal conductivity diamond film for semiconductors with high comprehensive performance through substrate preparation and surface treatment, high-density preferentially oriented diamond grain nucleation, periodic nucleation + diamond film deposition, substrate and diamond film separation, and surface grinding, polishing and cleaning. This method is simple to operate, low in cost, low in energy consumption and high in efficiency. The electrical, thermal and mechanical properties of the prepared high thermal conductivity diamond film for semiconductors are synergistically improved, which is conducive to large-scale industrial production and promotion. Attached Figure Description

[0043] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0044] Figure 1 This is a schematic diagram of the substrate and diamond film used for diamond film deposition in a method for preparing a high thermal conductivity diamond film substrate for semiconductors according to the present invention. In this diagram, reference numeral 1 represents the substrate for depositing the diamond film, and reference numeral 2 represents the diamond film.

[0045] Figure 2 This is a schematic cross-sectional view of the deposited diamond film from the nucleation plane to the growth plane in the preparation method of a high thermal conductivity diamond film substrate for semiconductors according to the present invention. In this view, reference numeral 1 represents the nucleated high density preferred orientation diamond grain layer, reference numeral 2 represents the deposited high density preferred orientation diamond grain layer, and reference numeral 3 represents the periodic nucleated grain.

[0046] Figure 3 This is an XRD diagram of the nucleation surface grains after the polycrystalline diamond film deposition is completed in a method for preparing a high thermal conductivity diamond film substrate for semiconductors according to Embodiment 1 of the present invention.

[0047] Figure 4This is a schematic diagram of the surface AFM of the polycrystalline diamond film after polishing in the preparation method of a high thermal conductivity diamond film substrate for semiconductors according to Embodiment 1 of the present invention. Detailed Implementation

[0048] The technical solution of the present invention will now be described with reference to the accompanying drawings.

[0049] In embodiments of the present invention, words such as "exemplarily," "for example," etc., are used to indicate that something is an example, illustration, or description. Any embodiment or design described as "exemplary" in the present invention should not be construed as being more preferred or advantageous than other embodiments or designs. Specifically, the use of the word "exemplary" is intended to present the concept in a concrete manner. Furthermore, in embodiments of the present invention, the meaning expressed by "and / or" can be both, or either one.

[0050] In the embodiments of the present invention, the terms "image" and "picture" may sometimes be used interchangeably. It should be noted that when the distinction is not emphasized, their intended meanings are consistent.

[0051] In this embodiment of the invention, sometimes a subscript such as W1 may be written in a non-subscript form such as W1. When the difference is not emphasized, the meaning they express is the same.

[0052] To make the technical problems, technical solutions and advantages of the present invention clearer, a detailed description will be given below in conjunction with the accompanying drawings and specific embodiments.

[0053] A method for preparing a high thermal conductivity diamond film substrate for semiconductors, wherein the method for preparing a high thermal conductivity diamond film substrate for semiconductors combines... Figure 1 and Figure 2 Includes the following steps:

[0054] S1. Substrate preparation and surface treatment: First, the substrate on which the diamond film is deposited is surface treated. Then, a nanodiamond suspension is used to electrostatically seed diamonds on the substrate surface. Finally, the surface-treated substrate is cleaned and dried to obtain the surface-treated substrate.

[0055] S2. High-density preferred orientation grain nucleation: The substrate with surface treatment completed in S1 is placed in a chemical vapor deposition apparatus, vacuumed, and heated. After heating to the preferred orientation grain nucleation temperature, high-density preferred orientation diamond grain nucleation is performed on the substrate surface. After nucleation, the methane gas flow rate is adjusted to 1-3% of the total gas flow rate, and 0.1-0.3% carbon dioxide gas is introduced simultaneously. High-density grain growth of the nucleation layer is performed on the basis of the high-density preferred orientation diamond grain, resulting in a high-density nucleation layer on the substrate surface.

[0056] S3, Periodic nucleation + diamond film deposition: Deposit diamond on the high-density nucleation layer on the substrate surface of S2 for 12-24 hours, and then start periodic nucleation and diamond film deposition to obtain a substrate with a diamond film layer.

[0057] S4. Separation of substrate from diamond film: Cool down the substrate with diamond film layer from S3, turn off the machine, and after cooling to room temperature, separate the substrate from the diamond film to obtain a diamond film with diamond nucleation layer.

[0058] S5. Surface grinding, polishing and cleaning: The surface of the nucleation layer of the diamond film with diamond nucleation layer in S3 is mechanically ground and polished, and the polished diamond film is cleaned to finally obtain a high thermal conductivity diamond film substrate for semiconductors.

[0059] Specifically, the diameter of the substrate in S1 is 100-200mm and the height is 10-50mm; the substrate includes ordinary commercial graphite substrate, Mo substrate and Si substrate. The following are the surface treatment methods for the three substrates: 1) Ordinary commercial graphite substrate: After the ordinary commercial graphite substrate is planarized, a Ti metal transition layer is deposited on the surface. Metal Ti is sputtered using a magnetron sputtering instrument for 10-15 minutes, with Ar as the protective gas. Then, annealing heat treatment is performed in a vacuum furnace for 30-40 minutes at a temperature controlled at 800-900℃, and the furnace is cooled. 2) Mo substrate and Si substrate: The substrate surface is planarized and polished.

[0060] Specifically, the diamond electrostatic seeding process in S1 is as follows: the substrate with deposited diamond film is immersed in a nanodiamond suspension with a concentration of 2.5-5.0 wt%, and removed after standing for 15-20 minutes; the cleaning and drying process is as follows: anhydrous ethanol is used for cleaning to rinse away the diamond residue on the substrate surface; the drying process involves placing the substrate in a resistance furnace, heating it at 150-180℃ for 120-180 minutes, and then cooling it with the furnace.

[0061] Specifically, the chemical vapor deposition apparatus in S2 includes a DC arc plasma CVD apparatus, a microwave plasma CVD apparatus, and a hot filament CVD apparatus; vacuuming and substrate heating: after evacuating the deposition apparatus chamber to less than 0.5 Pa, pure hydrogen gas with a purity of 99.9999% or higher is introduced at 1-7000 sccm, and argon gas at 0-7000 sccm. The power and chamber pressure are adjusted, and the chamber pressure is maintained at 3.0-12.0 kPa. The substrate is heated at a rate of 3-5 °C / min.

[0062] Specifically, the nucleation temperature for the preferred orientation grains in S2 is 820-860℃; the nucleation process for high-density preferred orientation diamond grains is as follows: 1) Nucleation of <110> oriented grains: The substrate temperature is raised to 820-830℃, and 2-3% of the total gas flow rate of methane is introduced to perform high-density grain nucleation for 30-40 minutes, maintaining the temperature at 850-860℃, and the grain thickness reaches 10-20μm; 2) Nucleation of <100> oriented grains: In a chemical vapor deposition system... A tungsten electrode is designed below the plasma discharge cathode. A DC pulse power supply with a voltage of 200-300V and a current of 1-2A is connected between the substrate and the tungsten electrode. The substrate is connected to the cathode, and the tungsten electrode is connected to the anode of the pulse power supply. The substrate temperature is raised to 820-830℃, and 2-3% of methane in the total gas flow rate is introduced to carry out nucleation for 20-30 minutes. The temperature is maintained at 850-860℃, and the grain thickness reaches 10-20μm. After nucleation is completed, the pulse power supply is turned off.

[0063] Specifically, the growth conditions for high-density grains in the nucleation layer of S2 are as follows: maintain the flow rates of pure hydrogen and argon at a constant level, change the flow rate of methane to 1-3% of the total gas flow rate, and simultaneously introduce 0.1-0.3% carbon dioxide gas, adjust the cavity pressure to maintain 3.0-12.0 kPa, and keep the substrate temperature above 1100°C for diamond deposition for 12-24 hours.

[0064] Specifically, the periodic nucleation and deposition process of the diamond film in S3 is as follows: after the dense grains of the nucleation layer grow for 12-24 hours, periodic nucleation begins, with an interval of 24-36 hours between two nucleations. Methane at 2.5-4% of the total gas flow rate is used for nucleation for 30-40 minutes. After one nucleation, the methane is adjusted to 1.3-1.5% of the total gas flow rate for deposition for 4-8 hours, and then the methane is adjusted to 1-1.3% of the total gas flow rate for deposition until the next nucleation. This process is repeated several times, with a total deposition time of 300-600 hours, resulting in a diamond film thickness greater than 1 mm. Throughout the process, 0.1-0.3% carbon dioxide gas is introduced and kept constant.

[0065] Specifically, the interlayer structure of the substrate with diamond film in S3 consists of a 10-20 μm thick <110> / <100> oriented high-density nucleation grain layer and a 70-120 μm thick <110> / <100> oriented high-density grain layer. After the formation of the high-density nucleation grain layer, a short-term high-concentration methane grain layer growth is performed to ensure that the nucleation surface remains <110> / <100> oriented after grinding and polishing, thereby reducing surface stress and surface porosity and improving surface quality.

[0066] Specifically, the cooling process in S4 is as follows: after the diamond film thickness is greater than 1mm, the power of the device is reduced by decreasing the current, and the cooling rate is controlled at 1-3℃ / min, so that the temperature is reduced by 30-50℃, and then held for 30-50min.

[0067] Specifically, the interlayer structure of the diamond film with diamond nucleation layer in S4 consists of a 10-20 μm thick <110> / <100> oriented high-density nucleation grain layer, a 70-120 μm thick <110> / <100> oriented high-density grain layer, and an 800-1500 μm thick periodic nucleation grain. The interlayer structure is deposited from the substrate upwards according to the process sequence.

[0068] Specifically, in S5, mechanical grinding and polishing is performed as follows: The diamond film growth surface is fixed on a grinding fixture, and the nucleation surface is thinned using W40 diamond micropowder with an average particle size of 30 μm, W20 diamond micropowder with an average particle size of 15 μm, W10 diamond micropowder with an average particle size of 10 μm, W5 diamond micropowder with an average particle size of 3.5 μm, and W1 diamond micropowder with an average particle size of 1 μm. Grinding is carried out for 0.5-2 hours to reduce coarse particles on the surface. During this time, the grinding disc rotation speed is 40-60 r / min, the linear velocity is 0.8-1.2 m / s, and the load pressure is 0.1 MPa. Then, the diamond film is placed in a polishing disc, and the nucleation surface is polished at a rotation speed of 1000-1200 r / min and a load of 0.20 MPa for 100-200 hours until the surface roughness is less than 1 nm.

[0069] Specifically, the cleaning process in S5 is as follows: boil the polished diamond film with concentrated H2SO4 and concentrated HNO3 in a volume ratio of 4:1 for 20-40 minutes; then rinse the surface with deionized water to remove residual acid, and then ultrasonically clean the sample with acetone and anhydrous ethanol for 10-30 minutes respectively, and then blow dry.

[0070] Specifically, the nucleation layer thickness of the high thermal conductivity diamond film substrate for semiconductors in S5 is reduced by 10-30 μm compared to that before mechanical polishing. The thermal conductivity of the high thermal conductivity diamond substrate for semiconductors is 2000-2300 W / m·K, the surface roughness Ra is 0.4-0.95 nm, and the resistivity is 8.5-56 × 10⁻⁶. 13 Ω·cm, flexural strength is 500-600MPa.

[0071] Example 1

[0072] This embodiment discloses a method for preparing a high thermal conductivity diamond film substrate for semiconductors, which includes the following steps:

[0073] S1. Substrate preparation and surface treatment: First, select a substrate with a diameter of 150mm and a height of 30mm for depositing diamond film. The substrate material is ordinary commercial graphite substrate. Perform surface treatment on the substrate. After planarizing the ordinary commercial graphite substrate, apply a Ti metal transition layer on the surface. Sputter Ti metal using a magnetron sputtering instrument for 15 minutes with Ar as the protective gas. Then, perform annealing heat treatment in a vacuum furnace for 30 minutes at a temperature controlled at 800℃, and cool with the furnace.

[0074] Then, a nanodiamond suspension was used to electrostatically seed diamonds onto the substrate surface on which the diamond film was deposited. The electrostatic seeding process was as follows: the substrate on which the diamond film was deposited was immersed in a nanodiamond suspension with a concentration of 2.5 wt%, and removed after standing for 15 minutes; the cleaning and drying process was as follows: anhydrous ethanol was used for cleaning to rinse away the diamond residue on the substrate surface; the substrate was placed in a resistance furnace and heated at 150°C for 120 minutes, and then cooled with the furnace.

[0075] Then the surface-treated substrate is cleaned and dried to obtain a surface-treated substrate;

[0076] S2. High-density preferential orientation grain nucleation: The substrate with surface treatment completed in S1 is placed in a DC arc plasma CVD device. After the deposition device chamber is evacuated to less than 0.5 Pa, pure hydrogen gas with a purity of 99.9999% or higher is introduced at 3600 sccm and argon gas at 3000 sccm. The power and chamber pressure are adjusted and the chamber pressure is maintained at 3.4 kPa. The substrate is heated at a rate of 3 °C / min.

[0077] After heating to the preferred orientation grain nucleation temperature of 825℃, high-density <110> oriented preferred orientation diamond grain nucleation was performed on the substrate surface: 250 sccm of methane was introduced to perform high-density grain nucleation for 30 min, and the temperature was maintained at 850-860℃, with the grain thickness reaching 10 μm.

[0078] After nucleation is complete, the high-density grain growth conditions of the nucleation layer are as follows: keep the flow rates of pure hydrogen and argon constant, change the flow rate of methane to 150 sccm, and simultaneously introduce carbon dioxide gas at 20 sccm. Adjust the cavity pressure to maintain 3.4 kPa, and keep the substrate temperature above 1100℃ for diamond deposition for 12 hours to obtain a high-density nucleation layer on the substrate surface.

[0079] S3. Periodic nucleation + diamond film deposition: Diamond is deposited on the high-density nucleation layer on the substrate surface in S2 for 12 hours. Then, periodic nucleation and diamond film deposition are performed, with a 24-hour interval between the two nucleation cycles. Nucleation is carried out for 30 minutes using 300 sccm of methane. After one nucleation cycle, the methane concentration is adjusted to 130 sccm for 4 hours, and then adjusted to 100 sccm for 19.5 hours until the next nucleation cycle. This process is repeated 15 times, with a total deposition time of 372.5 hours, resulting in a diamond film thickness of 1.6 mm. The carbon dioxide gas concentration is kept constant at 20 sccm throughout the process, resulting in a substrate with a diamond film layer.

[0080] S4. Substrate and diamond film separation: The substrate with diamond film layer in S3 is cooled down. The cooling process is as follows: after the diamond film thickness is greater than 1 mm, the power of the device is reduced by reducing the current. The cooling rate is controlled at 2℃ / min, so that the temperature is reduced by 50℃ and held for 30 min. Then the device is turned off. After cooling to room temperature, the substrate and diamond film are separated to obtain a diamond film with diamond nucleation layer.

[0081] The interlayer structure of the S3 and S4 substrates with diamond films consists of a 10 μm thick <110> oriented high-density nucleated grain layer, a 90 μm thick <110> oriented high-density grain layer, and a 1500 μm thick periodic nucleated grain layer, as shown below. Figure 3 As shown, XRD reveals that the nucleation surface (220) exhibits the highest preferred orientation.

[0082] S5. Surface Grinding, Polishing, and Cleaning: The nucleation layer surface of the diamond film with the diamond nucleation layer in S3 was mechanically ground and polished. The mechanical grinding and polishing process involved fixing the diamond film growth surface on a grinding fixture. The nucleation surface was thinned using W40 diamond micropowder with an average particle size of 30 μm, W20 diamond micropowder with an average particle size of 15 μm, W10 diamond micropowder with an average particle size of 10 μm, W5 diamond micropowder with an average particle size of 3.5 μm, and W1 diamond micropowder with an average particle size of 1 μm. Grinding was performed for 0.5 hours to reduce coarse surface particles. During this process, the grinding disc rotation speed was 40 r / min, the linear velocity was 0.8 m / s, and the load pressure was 0.1 MPa. Then, the diamond film was placed in a polishing disc, and the nucleation surface was polished at a rotation speed of 1200 r / min and a load of 0.20 MPa for 200 hours. Figure 4 As shown, in the AFM of the polycrystalline diamond nucleation surface after polishing, Ra = 0.428 nm in the 30×30 μm range;

[0083] The polished diamond film was cleaned using the following process: concentrated H2SO4 and concentrated HNO3 were boiled in a volume ratio of 4:1 for 20 minutes; then the surface was rinsed with deionized water to remove residual acid; then the sample was ultrasonically cleaned with acetone and anhydrous ethanol for 30 minutes respectively, and dried to obtain a high thermal conductivity diamond film substrate for semiconductors.

[0084] The nucleation layer thickness of the high thermal conductivity diamond film substrate for semiconductors prepared in this embodiment was reduced by 12 μm compared to that before mechanical grinding and polishing. The thermal conductivity of the high thermal conductivity diamond film substrate for semiconductors is 2214.1 W / m·K, the surface roughness Ra is 0.428 nm, and the resistivity is 27 × 10⁻⁶. 13 Ω·cm, with a bending strength of 593MPa.

[0085] Example 2

[0086] This embodiment discloses a method for preparing a high thermal conductivity diamond film substrate for semiconductors, which includes the following steps:

[0087] S1. Substrate preparation and surface treatment: First, select a substrate with a diameter of 120mm and a height of 20mm for depositing diamond film. The substrate material is Si substrate. The substrate surface is then smoothed and polished.

[0088] Then, a nanodiamond suspension was used to electrostatically seed diamonds onto the surface of the substrate on which the diamond film was deposited. The electrostatic seeding process was as follows: the substrate on which the diamond film was deposited was immersed in a nanodiamond suspension with a concentration of 2.5 wt%, and removed after standing for 20 minutes; the cleaning and drying process was as follows: anhydrous ethanol was used for cleaning to rinse away the diamond residue on the surface of the substrate; the substrate was placed in a resistance furnace and heated at 150°C for 120 minutes, and then cooled with the furnace.

[0089] Then the surface-treated substrate is cleaned and dried to obtain a surface-treated substrate;

[0090] S2. High-density preferential orientation grain nucleation: The substrate with surface treatment completed in S1 is placed in a microwave plasma CVD device. After the deposition device chamber is evacuated to less than 0.5 Pa, 1500 sccm of pure hydrogen gas with a purity of 99.9999% or higher and 0 sccm of argon gas are introduced. The power and chamber pressure are adjusted and the chamber pressure is maintained at 9.0 kPa. The substrate is heated at a rate of 3 °C / min.

[0091] After heating to the preferred orientation grain nucleation temperature of 825℃, high density <110> oriented diamond grain nucleation was performed on the substrate surface: 45 sccm of methane was introduced to perform high density grain nucleation for 40 min, and the temperature was maintained at 850-860℃, with the grain thickness reaching 10 μm.

[0092] After nucleation is completed, the high-density grain growth conditions of the nucleation layer are as follows: keep the pure hydrogen flow rate constant, change the methane flow rate to 36 sccm, and simultaneously introduce carbon dioxide gas at 3 sccm. Adjust the cavity pressure to 11 kPa and keep the substrate temperature above 1100°C for diamond deposition for 24 hours to obtain a high-density nucleation layer on the substrate surface.

[0093] S3, Periodic Nucleation + Diamond Film Deposition: Diamond is deposited on the high-density nucleation layer on the substrate surface of S2 for 24 hours. Then, periodic nucleation and diamond film deposition are performed, with a 24-hour interval between two nucleation cycles. Nucleation is carried out for 30 minutes using 50 sccm of methane. After one nucleation cycle, the methane concentration is adjusted to 24 sccm for 4 hours, then adjusted to 20 sccm for 19.5 hours, until the next nucleation cycle. This process is repeated 23 times, with a total deposition time of 576.5 hours and a diamond film thickness of 1.2 mm. The carbon dioxide gas concentration of 3 sccm is maintained constant throughout the process, resulting in a substrate with a diamond film layer.

[0094] S4. Substrate and diamond film separation: The substrate with diamond film layer in S3 is cooled down. The cooling process is as follows: after the diamond film thickness is greater than 1 mm, the power of the device is reduced by reducing the current, and the cooling rate is controlled at 1℃ / min to reduce the temperature by 50℃ and hold for 30 min. After cooling to room temperature, the substrate and diamond film are separated to obtain a diamond film with diamond nucleation layer.

[0095] The interlayer structure of diamond films with diamond nucleation layers in S3 and S4 consists of a 10 μm thick <110> oriented high-density nucleated grain layer, a 72 μm thick <110> oriented high-density grain layer, and a 1100 μm thick periodic nucleated grain.

[0096] S5. Surface Grinding, Polishing and Cleaning: The nucleation layer surface of the diamond film with diamond nucleation layer in S3 was mechanically ground and polished. The mechanical grinding and polishing process was as follows: the growth surface of the diamond film was fixed on the grinding fixture, and the nucleation surface was thinned by using W40 diamond micro powder with an average particle size of 30 μm, W20 diamond micro powder with an average particle size of 15 μm, W10 diamond micro powder with an average particle size of 10 μm, W5 diamond micro powder with an average particle size of 3.5 μm, and W1 diamond micro powder with an average particle size of 1 μm. Each was ground for 0.5 h to reduce coarse particles on the surface. At this time, the grinding disc rotation speed was 40 r / min, the linear velocity was 0.8 m / s, and the load pressure was 0.1 MPa. Then, the diamond film was placed in the polishing disc, and the nucleation surface was polished at a rotation speed of 1000 r / min and a load of 0.20 MPa for 100 h. The surface roughness Ra was 0.652 nm.

[0097] The polished diamond film was cleaned using the following process: concentrated H2SO4 and concentrated HNO3 were boiled in a volume ratio of 4:1 for 20 minutes; then the surface was rinsed with deionized water to remove residual acid; then the sample was ultrasonically cleaned with acetone and anhydrous ethanol for 10 minutes respectively, and dried to obtain a high thermal conductivity diamond film substrate for semiconductors.

[0098] The nucleation layer thickness of the high thermal conductivity diamond film substrate for semiconductors prepared in this embodiment was reduced by 13 μm compared to that before mechanical grinding and polishing. The thermal conductivity of the high thermal conductivity diamond film for semiconductors is 2253 W / m·K, and the resistivity is 42 × 10⁻⁶. 13 Ω·cm, flexural strength is 553MPa.

[0099] Example 3

[0100] This embodiment discloses a method for preparing a high thermal conductivity diamond film substrate for semiconductors, which includes the following steps:

[0101] S1. Substrate preparation and surface treatment: First, select a substrate with a diameter of 100mm and a height of 10mm for depositing diamond film. The substrate material is Si substrate. The substrate surface is then smoothed and polished.

[0102] Then, a nano-diamond suspension was used to electrostatically seed diamonds onto the surface of the substrate on which the diamond film was deposited. The electrostatic seeding process was as follows: the substrate on which the diamond film was deposited was immersed in a 3wt% nano-diamond suspension and left to stand for 20 minutes before being removed. The cleaning and drying process was as follows: anhydrous ethanol was used for cleaning to rinse away any diamond residue on the surface of the substrate. The drying process involved placing the substrate in a resistance furnace, heating it at 180°C for 180 minutes, and then cooling it with the furnace.

[0103] Then the surface-treated substrate is cleaned and dried to obtain a surface-treated substrate;

[0104] S2. High-density preferential orientation grain nucleation: The substrate with surface treatment completed in S1 is placed in a hot-wire CVD device. After evacuating the deposition device chamber to less than 0.5 Pa, pure hydrogen gas with a purity of 99.9999% or higher is introduced at 500 sccm and argon gas at 0 sccm. The power and chamber pressure are adjusted and the chamber pressure is maintained at 4.5 kPa. The substrate is heated at a rate of 3 °C / min.

[0105] After heating to the preferred orientation grain nucleation temperature of 825℃, high-density <110> oriented preferred orientation diamond grain nucleation was performed on the substrate surface: 15 sccm of methane was introduced to perform high-density grain nucleation for 40 min, and the temperature was maintained at 850-860℃, with the grain thickness reaching 13 μm.

[0106] After nucleation is completed, the high-density grain growth conditions of the nucleation layer are as follows: keep the pure hydrogen flow rate constant, change the methane flow rate to 11 sccm, and simultaneously introduce 1 sccm of carbon dioxide gas. Adjust the cavity pressure to 4.5 kPa and keep the substrate temperature above 1100°C for diamond deposition for 24 hours to obtain a high-density nucleation layer on the substrate surface.

[0107] S3, Periodic Nucleation + Diamond Film Deposition: Diamond is deposited on the high-density nucleation layer on the substrate surface of S2 for 24 hours. Then, periodic nucleation and diamond film deposition are performed, with a 24-hour interval between two nucleation cycles. Nucleation is carried out for 30 minutes using methane at 15 sccm. After one nucleation cycle, the methane concentration is adjusted to 8 sccm for 4 hours, and then adjusted to 7 sccm for 4 hours until the next nucleation cycle. This process is repeated 15 times, for a total deposition time of 372.5 hours, resulting in a diamond film thickness of 1.1 mm. Throughout the process, 0.1-0.3% carbon dioxide gas is introduced and kept constant. A substrate with a diamond film layer is obtained.

[0108] S4. Substrate and diamond film separation: The substrate with diamond film layer in S3 is cooled down. The cooling process is as follows: after the diamond film thickness is greater than 1 mm, the power of the device is reduced by reducing the current. The cooling rate is controlled at 2℃ / min, so that the temperature is reduced by 50℃ and held for 50 min; then the device is turned off; after cooling to room temperature, the substrate and diamond film are separated to obtain a diamond film with diamond nucleation layer.

[0109] The interlayer structure of the S3 and S4 substrates with diamond film layers consists of a 13 μm thick <110> oriented high-density nucleated grain layer, a 70 μm thick <110> oriented high-density grain layer, and a 1000 μm thick periodic nucleated grain.

[0110] S5. Surface Grinding, Polishing and Cleaning: The nucleation layer surface of the diamond film with diamond nucleation layer in S3 was mechanically ground and polished. The mechanical grinding and polishing process was as follows: the growth surface of the diamond film was fixed on the grinding fixture, and the nucleation surface was thinned by using W40 diamond micropowder with an average particle size of 30 μm, W20 diamond micropowder with an average particle size of 15 μm, W10 diamond micropowder with an average particle size of 10 μm, W5 diamond micropowder with an average particle size of 3.5 μm and W1 diamond micropowder with an average particle size of 1 μm. Each was ground for 0.5 h to reduce coarse particles on the surface. At this time, the grinding disc rotation speed was 40 r / min, the linear velocity was 0.8 m / s, and the load pressure was 0.1 MPa. Then, the diamond film was placed in the polishing disc, and the nucleation surface was polished at a rotation speed of 1000 r / min and a load of 0.20 MPa for 100 h, with a surface roughness of 0.928 nm.

[0111] The polished diamond film was cleaned using the following process: concentrated H2SO4 and concentrated HNO3 were boiled in a volume ratio of 4:1 for 40 minutes; then the surface was rinsed with deionized water to remove residual acid; then the sample was ultrasonically cleaned with acetone and anhydrous ethanol for 30 minutes respectively, and dried to obtain a high thermal conductivity diamond film substrate for semiconductors.

[0112] The nucleation layer thickness of the high thermal conductivity diamond film substrate for semiconductors prepared in this embodiment was reduced by 17 μm compared to that before mechanical grinding and polishing. The thermal conductivity of the high thermal conductivity diamond film substrate for semiconductors is 2002 W / m·K, the surface roughness Ra is 0.928 nm, and the resistivity is 9.2 × 10⁻⁶. 13 Ω·cm, flexural strength is 502MPa.

[0113] Example 4

[0114] This embodiment discloses a method for preparing a high thermal conductivity diamond film substrate for semiconductors, which includes the following steps:

[0115] S1. Substrate preparation and surface treatment: First, select a substrate with a diameter of 150mm and a height of 30mm for depositing diamond film. The substrate material is ordinary commercial graphite substrate. Perform surface treatment on the substrate. After planarizing the ordinary commercial graphite substrate, apply a Ti metal transition layer on the surface. Sputter Ti metal using a magnetron sputtering instrument for 15 minutes with Ar as the protective gas. Then, perform annealing heat treatment in a vacuum furnace for 30 minutes at a temperature controlled at 800℃, and cool with the furnace.

[0116] Then, a nanodiamond suspension was used to electrostatically seed diamonds onto the substrate surface on which the diamond film was deposited. The electrostatic seeding process was as follows: the substrate on which the diamond film was deposited was immersed in a nanodiamond suspension with a concentration of 2.5 wt%, and removed after standing for 15 minutes; the cleaning and drying process was as follows: anhydrous ethanol was used for cleaning to rinse away the diamond residue on the substrate surface; the substrate was placed in a resistance furnace and heated at 150°C for 120 minutes, and then cooled with the furnace.

[0117] Then the surface-treated substrate is cleaned and dried to obtain a surface-treated substrate;

[0118] S2. High-density preferential orientation grain nucleation: The substrate with surface treatment completed in S1 is placed in a DC arc plasma CVD device. After the deposition device chamber is evacuated to less than 0.5 Pa, pure hydrogen gas with a purity of 99.9999% or higher is introduced at 3600 sccm and argon gas at 3000 sccm. The power and chamber pressure are adjusted and the chamber pressure is maintained at 3.4 kPa. The substrate is heated at a rate of 3 °C / min.

[0119] After heating to the preferred orientation grain nucleation temperature of 822℃, high-density <100> oriented preferred orientation diamond grain nucleation was performed on the substrate surface: a tungsten electrode was designed below the plasma discharge cathode of the chemical vapor deposition equipment, and a DC pulse power supply with a voltage of 200V and a current of 1A was connected between the substrate and the tungsten electrode. The substrate was connected to the cathode, and the tungsten electrode was connected to the anode of the pulse power supply. The substrate temperature was raised to 825℃, and 250 sccm of methane was introduced to carry out nucleation for 30 minutes, maintaining the temperature at 850-860℃, and the grain thickness reached 15μm. After nucleation was completed, the pulse power supply was turned off.

[0120] After nucleation is complete, the high-density grain growth conditions of the nucleation layer are as follows: keep the flow rates of pure hydrogen and argon constant, change the flow rate of methane to 150 sccm, and simultaneously introduce carbon dioxide gas at 20 sccm. Adjust the cavity pressure to maintain 3.4 kPa, and keep the substrate temperature above 1100℃ for diamond deposition for 12 hours to obtain a high-density nucleation layer on the substrate surface.

[0121] S3. Periodic nucleation + diamond film deposition: Diamond is deposited on the high-density nucleation layer on the substrate surface in S2 for 12 hours. Then, periodic nucleation and diamond film deposition are performed, with a 24-hour interval between two nucleation cycles. Nucleation is carried out for 30 minutes using 300 sccm of methane. After one nucleation cycle, the methane concentration is adjusted to 130 sccm for 4 hours, and then adjusted to 100 sccm for 19.5 hours until the next nucleation cycle. This process is repeated 15 times, with a total deposition time of 372.5 hours, resulting in a diamond film thickness of 1.5 mm. Throughout the process, the carbon dioxide gas concentration is kept constant at 20 sccm. A substrate with a diamond film layer is obtained.

[0122] S4. Substrate and diamond film separation: The substrate with diamond film layer in S3 is cooled down. The cooling process is as follows: after the diamond film thickness is greater than 1 mm, the power of the device is reduced by reducing the current. The cooling rate is controlled at 2℃ / min, so that the temperature is reduced by 50℃ and held for 30 min. Then the device is turned off. After cooling to room temperature, the substrate and diamond film are separated to obtain a diamond film with diamond nucleation layer.

[0123] The interlayer structure of the S3 and S4 substrates with diamond film layers consists of a 15 μm thick <100> oriented high-density nucleated grain layer, a 95 μm thick <100> oriented high-density grain layer, and a 1400 μm thick periodic nucleated grain layer.

[0124] S5. Surface Grinding, Polishing, and Cleaning: The nucleation layer surface of the diamond film with the diamond nucleation layer in S3 was mechanically ground and polished. The mechanical grinding and polishing process was as follows: The diamond film growth surface was fixed on a grinding fixture, and the nucleation surface was thinned using W40 diamond micropowder with an average particle size of 30 μm, W20 diamond micropowder with an average particle size of 15 μm, W10 diamond micropowder with an average particle size of 10 μm, W5 diamond micropowder with an average particle size of 3.5 μm, and W1 diamond micropowder with an average particle size of 1 μm. Each was ground for 0.5 h to reduce coarse particles on the surface. During this time, the grinding disc rotation speed was 40 r / min, the linear velocity was 0.8 m / s, and the load pressure was 0.1 MPa. Then, the diamond film was placed in a polishing disc, and the nucleation surface was polished at a rotation speed of 1200 r / min and a load of 0.20 MPa for 200 h. The surface roughness Ra was 0.858 nm.

[0125] The polished diamond film was cleaned using the following process: concentrated H2SO4 and concentrated HNO3 were boiled in a volume ratio of 4:1 for 20 minutes; then the surface was rinsed with deionized water to remove residual acid; then the sample was ultrasonically cleaned with acetone and anhydrous ethanol for 30 minutes respectively, and dried to obtain a high thermal conductivity diamond film substrate for semiconductors.

[0126] The nucleation layer thickness of the high thermal conductivity diamond film substrate for semiconductors prepared in this embodiment was reduced by 16 μm compared to that before mechanical grinding and polishing. The thermal conductivity of the high thermal conductivity diamond film substrate for semiconductors is 2256 W / m·K, the surface roughness Ra is 0.858 nm, and the resistivity is 56 × 10⁻⁶. 13 Ω·cm, with a flexural strength of 563MPa.

[0127] Example 5

[0128] This embodiment discloses a method for preparing a high thermal conductivity diamond film substrate for semiconductors, which includes the following steps:

[0129] S1. Substrate preparation and surface treatment: First, select a substrate with a diameter of 150mm and a height of 30mm for depositing diamond film. The substrate material is Mo substrate. The substrate surface is then smoothed and polished.

[0130] Then, a nanodiamond suspension was used to electrostatically seed diamonds onto the substrate surface on which the diamond film was deposited. The electrostatic seeding process was as follows: the substrate on which the diamond film was deposited was immersed in a nanodiamond suspension with a concentration of 2.5 wt%, and removed after standing for 15 minutes; the cleaning and drying process was as follows: anhydrous ethanol was used for cleaning to rinse away the diamond residue on the substrate surface; the substrate was placed in a resistance furnace and heated at 150°C for 120 minutes, and then cooled with the furnace.

[0131] Then the surface-treated substrate is cleaned and dried to obtain a surface-treated substrate;

[0132] S2. High-density preferential orientation grain nucleation: The substrate with surface treatment completed in S1 is placed in a DC arc plasma CVD device. After the deposition device chamber is evacuated to less than 0.5 Pa, pure hydrogen gas with a purity of 99.9999% or higher is introduced at 3600 sccm and argon gas at 3000 sccm. The power and chamber pressure are adjusted and the chamber pressure is maintained at 3.4 kPa. The substrate is heated at a rate of 3 °C / min.

[0133] After heating to the preferred orientation grain nucleation temperature of 820-860℃, high-density <110> oriented preferred orientation diamond grain nucleation is performed on the substrate surface: 250 sccm of methane is introduced to perform high-density grain nucleation for 30 min, and the temperature is maintained at 850-860℃, with the grain thickness reaching 10 μm.

[0134] After nucleation is complete, the high-density grain growth conditions of the nucleation layer are as follows: keep the flow rates of pure hydrogen and argon constant, change the flow rate of methane to 150 sccm, and simultaneously introduce carbon dioxide gas at 20 sccm. Adjust the cavity pressure to maintain 3.4 kPa, and keep the substrate temperature above 1100℃ for diamond deposition for 12 hours to obtain a high-density nucleation layer on the substrate surface.

[0135] S3, Periodic Nucleation + Diamond Film Deposition: Diamond is deposited on the high-density nucleation layer on the substrate surface of S2 for 12 hours. Then, periodic nucleation and diamond film deposition are performed, with a 24-hour interval between the two nucleation cycles. Nucleation is carried out for 30 minutes using 300 sccm of methane. After one nucleation cycle, the methane flow rate is adjusted to 130 sccm for 4 hours of deposition, and then adjusted to 100 sccm of the total gas flow rate for 19.5 hours until the next nucleation cycle. The total deposition time is 372.5 hours, resulting in a diamond film thickness of 1.7 mm. Throughout the process, the carbon dioxide gas flow rate is kept constant at 20 sccm. A substrate with a diamond film layer is obtained.

[0136] S4. Delamination of substrate from diamond film: The substrate with diamond film layer in S3 is cooled down. The cooling process is as follows: after the diamond film thickness is greater than 1 mm, the power of the device is reduced by reducing the current, and the cooling rate is controlled at 2℃ / min to reduce the temperature by 50℃ and hold for 30 min. After cooling to room temperature, the substrate is delamination from the diamond film to obtain a diamond film with diamond nucleation layer.

[0137] The interlayer structure of the S3 and S4 substrates with diamond film layers consists of a 10 μm thick <110> oriented high-density nucleated grain layer, a 105 μm thick <110> oriented high-density grain layer, and a 1600 μm thick periodic nucleated grain.

[0138] S5. Surface Grinding, Polishing and Cleaning: The nucleation layer surface of the diamond film with diamond nucleation layer in S3 was mechanically ground and polished. The mechanical grinding and polishing process was as follows: the growth surface of the diamond film was fixed on the grinding fixture, and the nucleation surface was thinned by using W40 diamond micropowder with an average particle size of 30 μm, W20 diamond micropowder with an average particle size of 15 μm, W10 diamond micropowder with an average particle size of 10 μm, W5 diamond micropowder with an average particle size of 3.5 μm, and W1 diamond micropowder with an average particle size of 1 μm. Each was ground for 0.5 h to reduce coarse particles on the surface. At this time, the grinding disc rotation speed was 40 r / min, the linear velocity was 0.8 m / s, and the load pressure was 0.1 MPa. Then, the diamond film was placed in the polishing disc, and the nucleation surface was polished at a rotation speed of 1000 r / min and a load of 0.20 MPa for 180 h. The surface roughness Ra was 0.702 nm.

[0139] The polished diamond film was cleaned using the following process: concentrated H2SO4 and concentrated HNO3 were boiled in a volume ratio of 4:1 for 20 minutes; then the surface was rinsed with deionized water to remove residual acid; then the sample was ultrasonically cleaned with acetone and anhydrous ethanol for 30 minutes respectively, and dried to obtain a high thermal conductivity diamond film substrate for semiconductors.

[0140] The nucleation layer thickness of the high thermal conductivity diamond film substrate for semiconductors prepared in this embodiment was reduced by 15 μm compared to that before mechanical grinding and polishing. The thermal conductivity of the high thermal conductivity diamond film substrate for semiconductors is 2098 W / m·K, the surface roughness Ra is 0.702 nm, and the resistivity is 9.2 × 10⁻⁶. 13 Ω·cm, with a bending strength of 526MPa.

[0141] Example 6

[0142] This embodiment discloses a method for preparing a high thermal conductivity diamond film substrate for semiconductors, which includes the following steps:

[0143] S1. Substrate preparation and surface treatment: First, select a substrate with a diameter of 120mm and a height of 20mm for depositing diamond film. The substrate material is Si substrate. The substrate surface is then smoothed and polished.

[0144] Then, a nanodiamond suspension was used to electrostatically seed diamonds onto the surface of the substrate on which the diamond film was deposited. The electrostatic seeding process was as follows: the substrate on which the diamond film was deposited was immersed in a nanodiamond suspension with a concentration of 2.5 wt%, and removed after standing for 20 minutes; the cleaning and drying process was as follows: anhydrous ethanol was used for cleaning to rinse away the diamond residue on the surface of the substrate; the substrate was placed in a resistance furnace and heated at 150°C for 120 minutes, and then cooled with the furnace.

[0145] Then the surface-treated substrate is cleaned and dried to obtain a surface-treated substrate;

[0146] S2. High-density preferential orientation grain nucleation: The substrate with surface treatment completed in S1 is placed in a hot-wire CVD device. After evacuating the deposition device chamber to less than 0.5 Pa, pure hydrogen gas with a purity of 99.9999% or higher is introduced at 1500 sccm and argon gas at 0 sccm. The power and chamber pressure are adjusted and the chamber pressure is maintained at 9.0 kPa. The substrate is heated at a rate of 3 °C / min.

[0147] After heating to the preferred orientation grain nucleation temperature of 825℃, high-density <110> oriented diamond grain nucleation was performed on the substrate surface: a tungsten electrode was designed below the plasma discharge cathode of the chemical vapor deposition equipment, and a DC pulse power supply with a voltage of 300V and a current of 2A was connected between the substrate and the tungsten electrode. The substrate was connected to the cathode, and the tungsten electrode was connected to the anode of the pulse power supply. The substrate temperature was raised to 8225℃, and 45 sccm of methane was introduced to carry out nucleation for 30 min. The temperature was maintained at 850-860℃, and the grain thickness reached 19μm. After the nucleation was completed, the pulse power supply was turned off.

[0148] After nucleation is completed, the high-density grain growth conditions of the nucleation layer are as follows: keep the flow rates of pure hydrogen and argon constant, change the flow rate of methane to 36 sccm, and simultaneously introduce 3 sccm of carbon dioxide gas. Adjust the cavity pressure to 11 kPa and keep the substrate temperature above 1100°C for diamond deposition for 24 hours to obtain a high-density nucleation layer on the substrate surface.

[0149] S3, Periodic Nucleation + Diamond Film Deposition: Diamond is deposited on the high-density nucleation layer on the substrate surface of S2 for 24 hours. Then, periodic nucleation and diamond film deposition are performed, with a 24-hour interval between two nucleation cycles. Nucleation is carried out for 30 minutes using 50 sccm of methane. After one nucleation cycle, the methane concentration is adjusted to 24 sccm for 4 hours, then adjusted to 20 sccm for 19.5 hours, until the next nucleation cycle. This process is repeated 24 times, with a total deposition time of 600 hours and a diamond film thickness of 1.3 mm. The carbon dioxide gas concentration of 3 sccm is maintained constant throughout the process, resulting in a substrate with a diamond film layer.

[0150] S4. Delamination of substrate from diamond film: The substrate with diamond film layer in S3 is cooled down. The cooling process is as follows: after the diamond film thickness is greater than 1 mm, the power of the device is reduced by reducing the current, and the cooling rate is controlled at 1℃ / min to reduce the temperature by 50℃. The temperature is then held for 50 min. The device is then turned off. After the temperature drops to room temperature, the substrate is delamination from the diamond film to obtain a diamond film with a diamond nucleation layer.

[0151] The interlayer structure of diamond films with diamond nucleation layers in S3 and S4 consists of a 19 μm thick <100> oriented high-density nucleated grain layer, an 83 μm thick <110> oriented high-density grain layer, and a 1200 μm thick periodic nucleated grain.

[0152] S5. Surface Grinding, Polishing and Cleaning: The nucleation layer surface of the diamond film with diamond nucleation layer in S3 was mechanically ground and polished. The mechanical grinding and polishing process was as follows: the growth surface of the diamond film was fixed on the grinding fixture, and the nucleation surface was thinned by using W40 diamond micropowder with an average particle size of 30 μm, W20 diamond micropowder with an average particle size of 15 μm, W10 diamond micropowder with an average particle size of 10 μm, W5 diamond micropowder with an average particle size of 3.5 μm and W1 diamond micropowder with an average particle size of 1 μm. Each was ground for 0.5 h to reduce coarse particles on the surface. At this time, the grinding disc rotation speed was 50 r / min, the linear speed was 1 m / s, and the load pressure was 0.1 MPa. Then, the diamond film was placed in the polishing disc, and the nucleation surface was polished at a rotation speed of 1000 r / min and a load of 0.20 MPa for 150 h. The surface roughness Ra was 0.523 nm.

[0153] The polished diamond film was cleaned using the following process: concentrated H2SO4 and concentrated HNO3 were boiled in a volume ratio of 4:1 for 20 minutes; then the surface was rinsed with deionized water to remove residual acid; then the sample was ultrasonically cleaned with acetone and anhydrous ethanol for 30 minutes respectively, and dried to obtain a high thermal conductivity diamond film substrate for semiconductors.

[0154] The nucleation layer thickness of the high thermal conductivity diamond film substrate for semiconductors prepared in this embodiment was reduced by 16 μm compared to that before mechanical grinding and polishing. The thermal conductivity of the high thermal conductivity diamond film for semiconductors is 2296 W / m·K, the surface roughness Ra is 0.523 nm, and the resistivity is 56 × 10⁻⁶. 13 Ω·cm, with a bending strength of 592MPa.

[0155] The present invention proposes a method for preparing a high thermal conductivity diamond film substrate for semiconductors. By increasing the grain density on the nucleation surface, refining the grains, reducing surface defects and residual stress, and performing high-frequency periodic nucleation during the diamond film growth stage, the traditional columnar crystal growth pattern of diamond films is broken, and equiaxed crystal growth is achieved, thereby improving the overall quality of the diamond film and reducing diamond defects. Therefore, it can solve the technical problems existing in the CVD method for preparing polycrystalline diamond substrates, such as poor crystal quality leading to low thermal conductivity, numerous surface pores after polishing, poor flatness, and high surface stress.

[0156] This invention selects a wide range of substrates and deposition equipment for depositing diamond films. The substrates for depositing diamond films include graphite substrates, Mo substrates and Si substrates. The deposition equipment includes DC arc plasma jet CVD (DC arc plasma jet CVD) devices, microwave plasma CVD (MPCVD) devices and hot filament CVD (HFCVD) devices. It is widely applicable and the process is simple and controllable.

[0157] The method of this invention achieves self-peeling of diamond film from substrate by treating the substrate surface and depositing Ti on graphite substrate; it also achieves self-peeling of diamond film from substrate by polishing Mo and Si substrates, thereby improving preparation efficiency and success rate.

[0158] The method of the present invention performs diamond electrostatic seeding on the substrate surface, forming uniform micro-scratches on the substrate surface, which facilitates subsequent diamond deposition and improves the uniformity of diamond growth.

[0159] The method of this invention enables the formation of 10-20 μm <110> oriented grains on a substrate by nucleating high-density preferentially oriented diamond grains at 820-830°C with 2-3% methane of the total gas flow rate; and by using bias nucleation technology at 820-830°C with 2-3% methane of the total gas flow rate, the formation of 10-20 μm <100> oriented grains on a substrate.

[0160] The method of this invention involves growing the grains in 1-3% methane for 12-24 hours after nucleation, while simultaneously introducing 0.1-0.3% carbon dioxide gas. This results in a high-density, preferentially oriented grain layer of 80-140 μm. After grinding and polishing, the surface remains in the <110> / <100> orientation, resulting in a polished surface with low surface stress, reduced surface porosity, and a roughness as low as 1 nm. The carbon dioxide gas can also etch and refine the grains.

[0161] The method of this invention, through periodic nucleation and diamond film deposition, can reduce the competitive growth of grains during diamond growth, which leads to grain coarsening, thereby reducing internal defects in the diamond and improving the overall quality of the diamond film.

[0162] The method of the present invention can completely obtain a crack-free self-supporting diamond film by peeling the substrate from the diamond film.

[0163] The method of the present invention, through surface grinding, polishing and cleaning, can obtain a clean and uncontaminated high-grain density, low surface roughness, low surface defects and low surface residual stress high thermal conductivity semiconductor diamond substrate.

[0164] In summary, compared with traditional methods, the method of this invention prepares a high thermal conductivity diamond film for semiconductors with high comprehensive performance through substrate preparation and surface treatment, high-density preferentially oriented diamond grain nucleation, periodic nucleation + diamond film deposition, substrate and diamond film separation, and surface grinding, polishing and cleaning. This method is simple to operate, low in cost, low in energy consumption and high in efficiency. The electrical, thermal and mechanical properties of the prepared high thermal conductivity diamond film for semiconductors are synergistically improved, which is conducive to large-scale industrial production and promotion.

[0165] It should be understood that the term "and / or" in this article is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. A and B can be singular or plural. Additionally, the character " / " in this article generally indicates an "or" relationship between the preceding and following related objects, but it can also represent an "and / or" relationship. Please refer to the context for a more accurate understanding.

[0166] In this invention, "at least one" means one or more, and "more than one" means two or more. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of a single item or a plurality of items. For example, at least one of a, b, or c can represent: a, b, c, ab, ac, bc, or abc, where a, b, and c can be a single item or multiple items.

[0167] It should be understood that, in various embodiments of the present invention, the order of the above-mentioned process numbers does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.

[0168] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for preparing a high thermal conductivity diamond film substrate for semiconductors, characterized in that, The method for preparing the high thermal conductivity diamond film substrate for semiconductors includes the following steps: S1. Substrate preparation and surface treatment: First, the substrate on which the diamond film is deposited is surface treated. Then, a nanodiamond suspension is used to electrostatically seed diamonds on the substrate surface. Finally, the surface-treated substrate is cleaned and dried to obtain the surface-treated substrate. S2. High-density preferred orientation grain nucleation: The substrate with surface treatment completed in S1 is placed in a chemical vapor deposition apparatus, vacuumed, and heated. After heating to the preferred orientation grain nucleation temperature, high-density preferred orientation diamond grain nucleation is performed on the substrate surface. After nucleation, the methane gas flow rate is adjusted to 1-3% of the total gas flow rate, and 0.1-0.3% carbon dioxide gas is introduced simultaneously. High-density grain growth of the nucleation layer is performed on the basis of the high-density preferred orientation diamond grain, resulting in a high-density nucleation layer on the substrate surface. S3, Periodic nucleation + diamond film deposition: Deposit diamond on the high-density nucleation layer on the substrate surface of S2 for 12-24 hours, and then start periodic nucleation and diamond film deposition to obtain a substrate with a diamond film layer. S4. Separation of substrate from diamond film: Cool down the substrate with diamond film layer from S3, turn off the machine, and after cooling to room temperature, separate the substrate from the diamond film to obtain a diamond film with diamond nucleation layer. S5. Surface grinding, polishing and cleaning: The surface of the nucleation layer of the diamond film with diamond nucleation layer in S3 is mechanically ground and polished, and the polished diamond film is cleaned to finally obtain a high thermal conductivity diamond film substrate for semiconductors.

2. The method for preparing a high thermal conductivity diamond film substrate for semiconductors according to claim 1, characterized in that, The diameter of the substrate in S1 is 100-200mm and the height is 10-50mm. The substrates include ordinary commercial graphite substrates, Mo substrates and Si substrates. The following are the surface treatment methods for the three substrates: 1) Ordinary commercial graphite substrates: After the ordinary commercial graphite substrate is planarized, a Ti metal transition layer is deposited on the surface. Metal Ti is sputtered using a magnetron sputtering instrument for 10-15 minutes with Ar as the protective gas. Then, annealing heat treatment is performed in a vacuum furnace for 30-40 minutes at a temperature controlled at 800-900℃, and the furnace is cooled. 2) Mo and Si substrates: The substrate surface is planarized and polished.

3. The method for preparing a high thermal conductivity diamond film substrate for semiconductors according to claim 1, characterized in that, The diamond electrostatic seeding process in S1 is as follows: the substrate with the deposited diamond film is immersed in a nanodiamond suspension with a concentration of 2.5-5.0wt%, and then removed after standing for 15-20 minutes. The cleaning and drying process is as follows: Anhydrous ethanol is used for cleaning to rinse away the diamond residue on the substrate surface; Drying involves placing the substrate in a resistance furnace and heating it at 150-180℃ for 120-180 minutes, followed by furnace cooling.

4. The method for preparing a high thermal conductivity diamond film substrate for semiconductors according to claim 1, characterized in that, The chemical vapor deposition apparatus in S2 includes a DC arc plasma CVD apparatus, a microwave plasma CVD apparatus, and a hot filament CVD apparatus. Vacuuming and substrate heating are performed as follows: After evacuating the deposition apparatus chamber to a vacuum level of less than 0.5 Pa, pure hydrogen gas with a purity of 99.9999% or higher is introduced at 1-7000 sccm, and argon gas at 0-7000 sccm. The power and chamber pressure are adjusted, maintaining the chamber pressure at 3.0-12.0 kPa, and the substrate is heated at a rate of 3-5 °C / min.

5. The method for preparing a high thermal conductivity diamond film substrate for semiconductors according to claim 1, characterized in that, The nucleation temperature for preferred orientation grains in S2 is 820-860℃; the nucleation process for high-density preferred orientation diamond grains is as follows: 1) Nucleation of <110> oriented grains: The substrate temperature is raised to 820-830℃, and 2-3% of the total gas flow rate of methane is introduced to perform high-density grain nucleation for 30-40 minutes, maintaining the temperature at 850-860℃, and the grain thickness reaches 10-20μm; 2) Nucleation of <100> oriented grains: In the plasma of a chemical vapor deposition equipment... A tungsten electrode is designed below the cathode of the daughter discharge. A DC pulse power supply with a voltage of 200-300V and a current of 1-2A is connected between the substrate and the tungsten electrode. The substrate is connected to the cathode, and the tungsten electrode is connected to the anode of the pulse power supply. The substrate temperature is raised to 820-830℃, and 2-3% of the total gas flow rate of methane is introduced to carry out nucleation for 20-30 minutes. The temperature is maintained at 850-860℃, and the grain thickness reaches 10-20μm. After the nucleation is completed, the pulse power supply is turned off.

6. The method for preparing a high thermal conductivity diamond film substrate for semiconductors according to claim 1, characterized in that, The growth conditions for high-density grains in the nucleation layer of S2 are as follows: keep the flow rates of pure hydrogen and argon constant, change the flow rate of methane to 1-3% of the total gas flow rate, and simultaneously introduce 0.1-0.3% carbon dioxide gas. Adjust the cavity pressure to maintain 3.0-12.0 kPa, and keep the substrate temperature above 1100°C for diamond deposition for 12-24 hours.

7. The method for preparing a high thermal conductivity diamond film substrate for semiconductors according to claim 1, characterized in that, The process of periodic nucleation and deposition of diamond film in S3 is as follows: After the dense grains of the nucleation layer grow for 12-24 hours, periodic nucleation begins, with an interval of 24-36 hours between two nucleation cycles. Methane at 2.5-4% of the total gas flow rate is used for nucleation for 30-40 minutes. After one nucleation cycle, the methane is adjusted to 1.3-1.5% of the total gas flow rate for deposition for 4-8 hours. Then, the methane is adjusted to 1-1.3% of the total gas flow rate for deposition until the next nucleation cycle. This process is repeated several times, with a total deposition time of 300-600 hours, to achieve a diamond film thickness greater than 1 mm. Throughout the process, 0.1-0.3% carbon dioxide gas is introduced and kept constant.

8. The method for preparing a high thermal conductivity diamond film substrate for semiconductors according to claim 1, characterized in that, The cooling process in S4 is as follows: after the diamond film thickness is greater than 1mm, the power of the device is reduced by reducing the current, and the cooling rate is controlled at 1-3℃ / min, so that the temperature is reduced by 30-50℃, and then held for 30-50min.

9. The method for preparing a high thermal conductivity diamond film substrate for semiconductors according to claim 1, characterized in that, In S5, mechanical grinding and polishing is performed as follows: The diamond film growth surface is fixed on a grinding fixture. The nucleation surface is thinned using W40 diamond micropowder with an average particle size of 30 μm, W20 diamond micropowder with an average particle size of 15 μm, W10 diamond micropowder with an average particle size of 10 μm, W5 diamond micropowder with an average particle size of 3.5 μm, and W1 diamond micropowder with an average particle size of 1 μm. Grinding is carried out for 0.5-2 hours to reduce coarse particles on the surface. During this time, the grinding disc rotation speed is 40-60 r / min, the linear velocity is 0.8-1.2 m / s, and the load pressure is 0.1 MPa. Then, the diamond film is placed in a polishing disc, and the nucleation surface is polished at a rotation speed of 1000-1200 r / min and a load of 0.20 MPa for 100-200 hours until the surface roughness is less than 1 nm.

10. The method for preparing a high thermal conductivity diamond film substrate for semiconductors according to claim 1, characterized in that, The cleaning process in S5 is as follows: Boil the polished diamond film with concentrated H2SO4 and concentrated HNO3 at a volume ratio of 4:1 for 20-40 minutes; then rinse the surface with deionized water to remove residual acid, and then ultrasonically clean the sample with acetone and anhydrous ethanol for 10-30 minutes respectively, and then blow dry.

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